Many articles and packages include or can include a line of weakness having one or more perforations to facilitate tearing the article or package. These perforations are typically provided in a straight line because providing nonlinear lines of weakness is costly and technically complex.
One particular problem relating to providing nonlinear lines of perforation is that of equipment wear. Perforating typically involves a perforating blade interacting with a counterpart such as another blade, an anvil, or a male or female counterpart. In addition, either the perforating blade or its counterpart has a plurality of teeth, thereby causing a line of perforations to be imparted on a web moving between the perforating blade and its counterpart. This consistent interaction between the perforating blade and its counterpart causes both components to wear over time. Because of the teeth, wear of the components will be uneven. For example, the non-toothed component will experience grooves where it interacts with the teeth. This localized wear necessitates replacing or repairing a component while it still has unworn, functional sections.
With shaped lines of perforations, uneven wear is more challenging. For example, one section of a straight perforating blade may consistently hit the apex of a shaped anvil, another section may consistently hit the side of the shape at a particular angle, while yet another section may not be aligned with the anvil at all because of the shape. In such example, the section of the blade interacting with the apex will wear much faster than the section that sees no interaction with the anvil, and will wear at a different rate that the section hitting the anvil's side. If the blade in this example comprised teeth, the teeth would experience different wear patterns due to their interactions with different sections of the shape. Likewise, sections of the shaped anvil would experience different wear patterns due to their interactions with different sections of the blade (i.e., the sections having teeth versus recessed areas between the teeth). Indeed, the varying angles of interaction may cause both the toothed component and the non-toothed component to experience uneven wear. The issue is even more pronounced when a blade and counterpart are not parallel, such as when a shape is helixed about a rotating roll causing even greater variation in the angles of interaction. Likewise, the problem is exasperated where the nonlinear shape also comprises a three-dimensional, shaped cross-section such as a triangle, trapezoid, etc., which also creates variation in the angles of interaction between the blade and its counterpart. As noted above, the resulting localized wear requires premature, piecemeal repair or replacement or complete replacement of components.
Separately, manufacturers often have multiple product lines and may desire to create differently shaped lines of weakness, or different perforation patterns, on those different products. Doing so often requires equipment or component changes, new equipment and/or separate machines. This can lead to higher costs and production delays.
Accordingly, there is a continuing unmet need to provide an improved perforating apparatus and method to manufacture a web with a shaped lined of weakness. In particular, there continues to be an unfulfilled need to provide an apparatus and method that minimizes uneven blade and/or counter component wear and reduces the need for equipment repairs and replacement. In addition, there is a need for an apparatus having greater flexibility and the ability to provide different patterns of perforations with little to no equipment modifications.